Special Senses

Question 0

Stimulus into Sensation

Answer 0

• all sense organ have common functional characteristics
• able to detect stimulus
• stimulus converted into nerve (electrical) impulse
• impulse perceived as sensation in CNS

Question 1

Classifying Sense Organs

Answer 1

General

• microscopic receptors widely distributed throughout body
• pain, temp., touch, pressure

Special

• grouped into localized areas
• smell, taste, hearing, equilibrium, vision

All

• encapsulated (covered) or unencapsulated (free, naked)
• also classified by type of stimulus that activates

Question 2

General Sense Organs

Answer 2

• found in every part of body-concentrated in skin
• don’t all respond to same type of stimulus
• free nerve endings (pain, touch, temp.)

Types:

• tactile (Meissner) Corpuscules-light touch
• Ruffini (Bulbous) Corpuscules-persistant touch/pressure
• Lamellar (Pacini) Corpuscules-deep pressure
• Bulboid Corpuscules-touch
• Golgi Tendon Organs-proprioception (tension)
• Muscle Spindles-proprioception (length)

Question 3

Sclera

Answer 3

• opaque white of the eye
• protective, thick connective tissue
• cornea
  
  • transparent window where light enters
  • change dramatically affects ability to focus
  • appears colourful because over iris
• conjuctiva
  
  • mucous membrane lining eyelids
  • covers sclera in front
  • kept moist by tears from lacrimal gland

Question 4

Choroid

Answer 4

• middle layer
• contains dark pigment to prevent light from scattering
• 2 involuntary muscles
  1) Iris (coloured part)
  2) Ciliary muscle
• pupil
  
  • black center of iris
  • constrict in bright light, dilate in dim light
• lens
  
  • directly behind pupil
  • allows to focus by bulging
  • loses ability throughout life–>cataracts (milky)

Question 5

Retina

Answer 5

• innermost layer
• contains rods (night vision, greys) and cones (daytime, colour, RBG)
• macula lutea
  
  • yellowish area near center
  • surrounds fovea centralis (greatest concentration of cones)
• inside full of fluids-bend light to focus on retina
  
  • aqueous humor–>watery fluid in front of lens
  • vitreous humor–>jellylike fluid behind lens

Question 6

Visual Pathway

Answer 6

• light is stimulus resulting in vision
• enters eye through pupil
• refracted as passes through cornea, aqueous humor, lens, vitreous humor and focuses on retina
• photoreceptors
  
  • rods and cones
  • produce nerve impulses
• impulse leaves retina through optic nerve
  
  • optic disc (area of retina where optic nerve fibers exit)
    
    • blind spot, no rods/cones present

Question 7

Equilibrium and Balance

Answer 7

• mechanoreceptors
• physical forces involving sound vibrations and fluid movements
  
  • initiate nerve impulses
  • perceived as sound and balance

Question 8

External Ear

Answer 8

• auricle-appendage on side of head
• external auditory canal
  
  • curving tube, 2.5cm
  • into temporal bone, ends at eardrum
• ceruminous glands prod. cerumen (wax)
• sound waves travel through canal, strike tympanic membrane, which then vibrates

Question 9

Middle Ear

Answer 9

• tiny, thin, epithelium-lined cavity, hollowed out of temporal bone
• 3 small bones (ossicles)
  
  • malleus, incus, stapes
• oval window
  
  • separates mid/inner ear
  • eardrum virates, causing bones to move and transmit vibration through middle ear
  • stapes moves vs. causing movement in fluid of inner ear
• auditory (eustachian) tube-connect throat with middle ear

Question 10

Inner Ear

Answer 10

• activation of mechanoreceptors generates nerve impulse
• 3 spaces in temporal bone, in complex maze (bony labyrinth)
  
  • filled with perilymph
  • vestibule, semicircular canals, cochlea

Question 11

Inner Ear-Crista ampullaris

Answer 11

• within ampulla of each semicircular canal
• specialized receptor
• generates nerve impulse when move head

Question 12

Inner Ear-Vestibular Nerve

Answer 12

• receptors in vestibule and semicircular canals joined
• further join with cochlea to form acoustic nerve
  
  • cranial nerve VIII

Question 13

Inner Ear-Organ of Corti

Answer 13

• organ of hearing
• lies in cochlea
• specialized hair cells generate nerve impulse when bent by movement of endolymph
• set in motion by sound waves

Question 14

Taste

Answer 14

• taste buds
  
  • supporting cells and chemoreceptors (gustatory cells)
  • generate taste impulses
• located on sides of bumps (papillae) on tongue and soft palate
• circumvallate papillae
  
  • large, contain most taste buds
  • form V at back of tongue
• each opens into trenchlike moat, filled with saliva
• chemicals dissolved in saliva, stimulate gustatory cells

Question 15

Smell

Answer 15

• olfactory receptors
  - specialized cilia sense different chemicals
  
  • respond by generating nerve impulses
• adaptation
  
  • cells develop fatigue and lose ability to respond
  • smells not sense after short exposure
• impulse travels through olfactory nerves, enter thalamus and relay to olfactory center in brain cortex
• closely associated with limbic area (memory and emotion) of brain